Generally, a thermally activated reserve battery (thermal battery), which does not exhibit battery performance at room temperature, is operated in such a manner that when an igniter of the battery begins to burn in response to an electrical signal applied thereto, a heat source between electrodes is ignited due to heat generated from the igniter to thereby melt a solid electrolyte due to heat produced from the heat source.
Such a thermally activated reserve battery is superior in terms of structural stability, reliability, and long-term storability.
Hence, the thermally activated reserve battery having the advantages described above is useful as an emergency power supply for civilian purposes and as a main or auxiliary power supply in the aerospace industry or for guided weapons for military purposes.
Since the thermally activated reserve battery is characterized in that the electrolyte thereof is not conductive at room temperature, it has no intrinsic energy loss and may thus be stored for a long period of time. Furthermore, this battery may be favorably used without deterioration of performance thereof even after long-term storage.
Devices using batteries have been developed in a trend of requiring a decrease in the volume of the battery and an increase in the capacity and output of the battery.
Accordingly, batteries are manufactured to be small and integrated. In particular, thorough research into energy density and high output of thermally activated reserve batteries is ongoing.
As studies for desired energy density and high output are carried out using new expensive electrode materials or by means of special processes or related instruments, economic loss and complicated processing are incurred. Furthermore, conventional electrode materials do not satisfy requirements of high energy density and high output.
A currently available thermal battery mainly includes an anode material such as LiSi, a cathode material such as FeS2, and an electrolyte composed of LiCl—KCl and LiBr—LiCl—LiF.
As for a LiSi/FeS2 thermal battery, however, the weight of LiSi (1,747 A·s/g) for an anode is smaller than that of FeS2 (1,206 A·s/g). Hence, the volume of LiSi has to be increased to achieve high battery capacity. In an electrochemical reaction, actual availability of LiSi becomes much lower due to phase change for FeS2, and thus limitations are imposed on using it as an anode material for a thermal battery requiring large capacity and high output.
To solve the problems of LiSi, LAN (Lithium anode) related patents published by CRC (Catalyst Research Center) disclose methods of using pure lithium having excellent capacity and output characteristics as known to date as an anode for a thermal battery in such a manner that it is added with an iron (Fe) powder binder to increase the viscosity of lithium at a temperature equal to or higher than the melting temperature (180° C.) of lithium. In some developed countries, thermal batteries having high energy density and high output density have been developed using such technology.
However, the above technology is problematic because lithium has to be mixed with about 80 wt % of iron powder to reduce melting of pure lithium, and thus the energy density thereof is remarkably decreased compared to theoretical lithium energy density.
Although some research into impregnation of a metal foam with lithium is ongoing, it is difficult to uniformly impregnate the metal foam with lithium upon actual application.
Moreover, even when the metal foam is impregnated with lithium, the resulting unit cell battery may undesirably short out attributed to leakage of lithium.